1. Field of the Invention
The invention relates to wireless modems, and more particularly, to a wireless modem having a sensor for sensing the presence of an external antenna connector and for configuring an electrical connection thereto from an RF signal component.
2. Description of the Related Art
Antennas that are internal to PC-Card wireless modems have limitations that typically provide worse performance than external antennas such as a traditional whip antenna. To get best overall performance from a modem with a built-in antenna, it is necessary to have a provision for an external antenna connection as well as the built-in antenna. The problem is that a method must be devised that will switch the correct antenna into play depending on whether the external antenna is installed or not. A second benefit of having an antenna switching method is that factory production test jigs can gain access to the modem antenna port via the external connector.
Prior art products such as AirCard™ AC580/AC5220™ from Sierra Wireless, Inc. have used an MC-Card type switched RF connector shown in FIG. 1. With this connector, when an external antenna cable is inserted, the AirCard™ internal antenna is disconnected from the RF front end by the MC-Card connector.
There may be several problems with the use of an MC-Card switched connector for the external antenna. For example, the MC-Card switched connector may be primarily designed as a factory test connector and may not be meant for use with external antenna and cables. The connector may not be mechanically strong enough to support an external antenna directly. A cabled connection must be used so that the connector is not stressed or impacted. Also, whip-antennas such as those of Sierra Wireless may have an SSMB type sub-miniature connector. The MC-Card connector is not compatible with SSMB. Therefore direct connectivity of those components is not possible. In addition, the conventional switched connector is not very reliable and will often stick and not switch over as it should. It may be sensitive to the heat of the soldering reflow process and can be damaged when the internal plastic insulation sleeve softened during reflow and the connector center pin shifted in the plastic. Finally, circuit board RF trace routing is not optimal with a switched connector because the signal trace must go first to the connector and then over the internal antenna. This long trace path to the internal antenna incurs signal loss.